A technique for suppressing changes in the seated posture of a vehicle occupant has been adopted in vehicle seatbelt devices installed for the purpose of protecting occupants sitting in seats in the vehicle, wherein the vehicle occupant is restrained by the seatbelt during an emergency or when the traveling state is unstable (during abnormal behavior).
A common seatbelt is comprised of a shoulder belt for restraining one shoulder of a vehicle occupant, and a lap belt for restraining the lap of the vehicle occupant. A tongue is provided between the shoulder belt and the lap belt so as to allow the belt to be inserted and moved therethrough. This tongue is installed so as to be capable of detaching from a buckle secured to an anchor. A seatbelt for simultaneously restraining one shoulder and the lap of the vehicle occupant can be wound up by a belt reel. A known example of such a seatbelt device for a vehicle is disclosed in Japanese Patent Application Laid-Open Publication No. 2000-118352.
In the vehicle seatbelt control device disclosed in the 2000-118352 publication, the torque of a motor is transmitted to a belt reel via a clutch, whereby the seatbelt is wound up by the belt reel. The clutch is capable of switching the transmitted torque between continuous and multiple stages in accordance with the manner in which the seatbelt is being used. The restraining force for restraining the vehicle occupant through the seatbelt is varied by the switching of the torque.
Frictional force is created in a reversing part of the belt against the tongue attached to the buckle. Thus, a problem remains with sufficiently taking up the slack in the lap belt by winding in one end of the seatbelt; i.e., the shoulder belt, by means of the belt reel. To deal with this problem, one considered option is that a pre-tensioner for taking in the slack of the lap belt be provided separate from the belt reel.
However, the slack in the lap belt is constantly being taken in. Since this causes the lap of the vehicle occupant to be constantly constricted by the lap belt, it is impractical to maintain a comfortable ride for the vehicle occupant.